1. Field of the Invention
The present invention relates to a paging method of performing individual calling and group calling, and also relates to a pager which can be called by this method.
2. Description of the Related Art
One paging method is disclosed in U.S. Pat. No. 4,403,212. In this method, a base station transmits an address-word signal including a calling code or calling number designating one of the pagers which can communicate with the base station, and then a message-word signal which is to be supplied to the pager designated by the calling number. Each pager has a memory (e.g., a ROM) storing the calling number assigned to the pager. Upon receipt of the calling number sent from the base station, the pager determines whether or not the received calling number is identical to the code stored in the memory. If the received number is identical to the stored one, the pager determines that it has been called, and generates an alarm, informing its bearer that the pager is being called. Then, the pager receives the message-word signal transmitted from the base station after the address-word signal. A display displays the message represented by the message-word signal
Another known paging method can perform not only the individual calling, but also so-called group calling. In this paging method, the memory of each pager stores two calling numbers, i.e., the individual-calling number assigned to the pager, and the group-calling number assigned to the group of pagers to which the pager belongs. In order to achieve the individual calling, a caller transmits the individual-calling number assigned to the pager to which he or she wishes to call to the base station. To perform the group calling, the caller transmits the group-calling number assigned to the group of pagers to which he or she wishes to call to the base station. This conventional paging method is disadvantageous in the following respect.
The caller cannot call the selected ones of the pagers belonging to a group, by using a group-calling number. He or she must repeat individual calling in order to call only the selected pagers of the group.
This problem can be solved by dividing the pagers of each group into subgroups each consisting of less pagers. Here arises another problem. A subgroup-calling number must be assigned to each pager, in addition to the individual-calling number and the group-calling number. The memory incorporated in the pager must have a large memory capacity great enough to store these calling numbers. Every time the pager receives calling number, the pager must compare received calling number with each of the calling numbers. It must therefore be complex in structure.
Moreover, still another problem arises if each of the groups is divided into sub-groups each consisting of less pagers. Assuming that a calling number is formed of a predetermined number of bits, for example, 18 bits, the paging system could have as many as 218 pagers if only one calling number were assigned to each pager. If two or more calling numbers, such as an individual-calling number and a group-calling number, are assigned to each pager, the paging system can have but far less pagers. In other words, the more calling numbers assigned to each pager, the less pagers the system can have.
This is why an individual-calling number and only one group-calling number are assigned to each pager in the conventional paging method. In the conventional paging method, it is impossible for the caller to call some of the pagers of a group at the same time.